1. Field of the Invention
The present invention relates to a display device, and more particularly, to a display device that can respond to occurrence of static electricity.
2. Discussion of the Related Art
With the advance of various portable electronic devices such as mobile communication terminals, smart phones, tablet computers, notebook computers, etc., the demand for flat panel display (FPD) devices applicable to the portable electronic devices is increasing. Liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission display (FED) devices, organic light emitting display devices, etc. are being actively researched as the FPD devices.
In such FPD devices, the application fields of liquid crystal display (LCD) devices are being expanded due to advanced manufacturing technology, an easily driven driver, a high-quality image, and a large screen.
Moreover, in such FPD devices, the organic light emitting display devices have a fast response time of 1 ms or less and low power consumption, and have no limitation in a viewing angle because the organic light emitting display devices self-emit light. Accordingly, the organic light emitting display devices are attracting much attention as next generation FPD devices.
FIG. 1 is a diagram illustrating a configuration of an electrostatic discharge (ESD) circuit 60 included in a related art display device, and FIG. 2 is a graph showing an electrical characteristic of a thin film transistor (TFT) configuring the ESD circuit 60 included in the related art display device.
The above-described FPD device (hereinafter simply referred to as a display device) includes a panel that includes a display area displaying an image and a non-display area formed outside the display area, a source driving integrated circuit (IC) that respectively supplies data voltages to a plurality of data lines formed in the display area, and a gate driving IC that supplies a scan signal to a plurality of gate lines formed in the display area.
Generally, static electricity occurs in electronic devices.
Therefore, as illustrated in FIG. 1, display devices include the ESD circuit 60 that prevents static electricity from occurring or prevents a damage caused by the static electricity.
The ESD circuit 60 extends from the source driving IC, and is coupled to a corresponding data line, formed in the display area, through a first non-display area. The ESD circuit 60 is provided in the first non-display area.
An end of one side of the ESD circuit 60 is coupled to a corresponding data line in the first non-display area in which the source driving IC is coupled to the panel, and as illustrated in FIG. 1, an end of the other side is coupled to a high-level driving voltage VDD terminal or a low-level driving voltage VSS terminal, or is coupled to a gate high voltage terminal (through which a gate high voltage VGH is supplied) or a gate low voltage terminal (through which a gate low voltage VGL is supplied)
The ESD circuit 60 is coupled between high voltage terminals (VDD and VSS) or low voltage terminals (VSS and VGL) and a corresponding data line which are formed in a display device such as an LCD device or an organic light emitting display device.
Therefore, when a voltage (static electricity) greater than a normal operation range is induced in the data line, among a plurality of the ESD circuits 60 illustrated in FIG. 1, the ESD circuit 60 which is coupled to the high-level driving voltage VDD terminal is turned on with the static electricity. Therefore, the high-voltage static electricity induced in the data line flows toward the high-level driving voltage VDD terminal, and thus, a data voltage Vdata applied to the data line is reduced to a normal state.
On the other hand, when a voltage (static electricity) less than a normal operation range is induced in the data line, among a plurality of the ESD circuits 60 illustrated in FIG. 1, the ESD circuit 60 which is coupled to the low-level driving voltage VSS terminal is turned on with the static electricity. Therefore, a current flows from the low-level driving voltage VSS terminal to the data line, and thus, the data voltage Vdata applied to the data line is increased to the normal state.
The ESD circuits 60 may be provided in a second non-display area facing the first non-display area, in addition to an upper end of the panel, namely, the first non-display area. That is, the ESD circuits 60 are respectively provided at the upper end and a lower end of the panel, and prevent a high voltage and a low voltage, which are generated from the static electricity, from being applied to the data line.
Each of the ESD circuits 60, as illustrated in FIG. 1, includes a TFT. When the ESD circuit 60 is used for a long time, the TFT is deteriorated, and for this reason, a threshold voltage Vth of the TFT is shifted.
That is, when the ESD circuit 60 is used for a long time, as shown in FIG. 2, the threshold voltage Vth of the TFT is shifted in a negative (−) direction, and for this reason, a leakage current occurs in the TFT.
For example, the TFT is formed in the display device, and in a case where the threshold voltage Vth for when the TFT starts to be driven is 3.9 V (see a graph (e) of FIG. 2), despite the data voltage Vdata of −10 V, a leakage current hardly flows in the TFT.
However, as the display device and the TFT are used for a long time, the threshold voltage Vth of the TFT shifts to −4.1 V (see curve (a) of FIG. 2) due to deterioration of the TFT. In this case, it can be seen that when the data voltage Vdata is −10 V, a leakage current of about 0.05E-05 flows in the TFT.
That is, in the related art display device, as the display device is used for a long time, the TFT configuring the ESD circuit 60 is deteriorated, and thus, the threshold voltage Vth of the TFT is shifted in the negative (−) direction. For this reason, even when a normal data voltage instead of static electricity flows to the data line, a leakage current flows through the ESD circuit 60.
Therefore, even in a normal state where static electricity does not occur, an amount of current applied to the data line is reduced, and thus, the panel cannot display an image having normal luminance, causing a degradation in a quality of the image.
Moreover, as described above, in the normal state, when a leakage current occurs in the ESD circuit 60, a normal current which flows to the data line formed in the display area is reduced. For this reason, a higher data voltage Vdata is applied to the data line, causing an increase in power consumption of the source driving IC.